/*
 * Copyright 2012 The Netty Project
 *
 * The Netty Project licenses this file to you under the Apache License,
 * version 2.0 (the "License"); you may not use this file except in compliance
 * with the License. You may obtain a copy of the License at:
 *
 *   http://www.apache.org/licenses/LICENSE-2.0
 *
 * Unless required by applicable law or agreed to in writing, software
 * distributed under the License is distributed on an "AS IS" BASIS, WITHOUT
 * WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied. See the
 * License for the specific language governing permissions and limitations
 * under the License.
 */
package io.netty.handler.codec.http;

import io.netty.buffer.ByteBuf;
import io.netty.channel.Channel;
import io.netty.channel.ChannelHandlerContext;
import io.netty.channel.ChannelPipeline;
import io.netty.channel.CombinedChannelDuplexHandler;
import io.netty.handler.codec.PrematureChannelClosureException;
import io.netty.util.ReferenceCountUtil;

import java.util.ArrayDeque;
import java.util.List;
import java.util.Queue;
import java.util.concurrent.atomic.AtomicLong;

/**
 * A combination of {@link HttpRequestEncoder} and {@link HttpResponseDecoder}
 * which enables easier client side HTTP implementation. {@link HttpClientCodec}
 * provides additional state management for <tt>HEAD</tt> and <tt>CONNECT</tt>
 * requests, which {@link HttpResponseDecoder} lacks. Please refer to
 * {@link HttpResponseDecoder} to learn what additional state management needs
 * to be done for <tt>HEAD</tt> and <tt>CONNECT</tt> and why
 * {@link HttpResponseDecoder} can not handle it by itself.
 *
 * If the {@link Channel} is closed and there are missing responses, a
 * {@link PrematureChannelClosureException} is thrown.
 *
 * @see HttpServerCodec
 */
public final class HttpClientCodec extends
        CombinedChannelDuplexHandler<HttpResponseDecoder, HttpRequestEncoder>
        implements HttpClientUpgradeHandler.SourceCodec
{

    /** A queue that is used for correlating a request and a response. */
    private final Queue<HttpMethod> queue = new ArrayDeque<HttpMethod>();

    /** If true, decoding stops (i.e. pass-through) */
    private boolean done;

    private final AtomicLong requestResponseCounter = new AtomicLong();

    private final boolean failOnMissingResponse;

    /**
     * Creates a new instance with the default decoder options
     * ({@code maxInitialLineLength (4096}}, {@code maxHeaderSize (8192)}, and
     * {@code maxChunkSize (8192)}).
     */
    public HttpClientCodec()
    {
        this(4096, 8192, 8192, false);
    }

    /**
     * Creates a new instance with the specified decoder options.
     */
    public HttpClientCodec(int maxInitialLineLength, int maxHeaderSize,
            int maxChunkSize)
    {
        this(maxInitialLineLength, maxHeaderSize, maxChunkSize, false);
    }

    /**
     * Creates a new instance with the specified decoder options.
     */
    public HttpClientCodec(int maxInitialLineLength, int maxHeaderSize,
            int maxChunkSize, boolean failOnMissingResponse)
    {
        this(maxInitialLineLength, maxHeaderSize, maxChunkSize,
                failOnMissingResponse, true);
    }

    /**
     * Creates a new instance with the specified decoder options.
     */
    public HttpClientCodec(int maxInitialLineLength, int maxHeaderSize,
            int maxChunkSize, boolean failOnMissingResponse,
            boolean validateHeaders)
    {
        init(new Decoder(maxInitialLineLength, maxHeaderSize, maxChunkSize,
                validateHeaders), new Encoder());
        this.failOnMissingResponse = failOnMissingResponse;
    }

    /**
     * Creates a new instance with the specified decoder options.
     */
    public HttpClientCodec(int maxInitialLineLength, int maxHeaderSize,
            int maxChunkSize, boolean failOnMissingResponse,
            boolean validateHeaders, int initialBufferSize)
    {
        init(new Decoder(maxInitialLineLength, maxHeaderSize, maxChunkSize,
                validateHeaders, initialBufferSize), new Encoder());
        this.failOnMissingResponse = failOnMissingResponse;
    }

    /**
     * Prepares to upgrade to another protocol from HTTP. Disables the
     * {@link Encoder}.
     */
    @Override
    public void prepareUpgradeFrom(ChannelHandlerContext ctx)
    {
        ((Encoder) outboundHandler()).upgraded = true;
    }

    /**
     * Upgrades to another protocol from HTTP. Removes the {@link Decoder} and
     * {@link Encoder} from the pipeline.
     */
    @Override
    public void upgradeFrom(ChannelHandlerContext ctx)
    {
        final ChannelPipeline p = ctx.pipeline();
        p.remove(this);
    }

    public void setSingleDecode(boolean singleDecode)
    {
        inboundHandler().setSingleDecode(singleDecode);
    }

    public boolean isSingleDecode()
    {
        return inboundHandler().isSingleDecode();
    }

    private final class Encoder extends HttpRequestEncoder
    {

        boolean upgraded;

        @Override
        protected void encode(ChannelHandlerContext ctx, Object msg,
                List<Object> out) throws Exception
        {

            if (upgraded)
            {
                out.add(ReferenceCountUtil.retain(msg));
                return;
            }

            if (msg instanceof HttpRequest && !done)
            {
                queue.offer(((HttpRequest) msg).method());
            }

            super.encode(ctx, msg, out);

            if (failOnMissingResponse)
            {
                // check if the request is chunked if so do not increment
                if (msg instanceof LastHttpContent)
                {
                    // increment as its the last chunk
                    requestResponseCounter.incrementAndGet();
                }
            }
        }
    }

    private final class Decoder extends HttpResponseDecoder
    {
        Decoder(int maxInitialLineLength, int maxHeaderSize, int maxChunkSize,
                boolean validateHeaders)
        {
            super(maxInitialLineLength, maxHeaderSize, maxChunkSize,
                    validateHeaders);
        }

        Decoder(int maxInitialLineLength, int maxHeaderSize, int maxChunkSize,
                boolean validateHeaders, int initialBufferSize)
        {
            super(maxInitialLineLength, maxHeaderSize, maxChunkSize,
                    validateHeaders, initialBufferSize);
        }

        @Override
        protected void decode(ChannelHandlerContext ctx, ByteBuf buffer,
                List<Object> out) throws Exception
        {
            if (done)
            {
                int readable = actualReadableBytes();
                if (readable == 0)
                {
                    // if non is readable just return null
                    // https://github.com/netty/netty/issues/1159
                    return;
                }
                out.add(buffer.readBytes(readable));
            }
            else
            {
                int oldSize = out.size();
                super.decode(ctx, buffer, out);
                if (failOnMissingResponse)
                {
                    int size = out.size();
                    for (int i = oldSize; i < size; i++)
                    {
                        decrement(out.get(i));
                    }
                }
            }
        }

        private void decrement(Object msg)
        {
            if (msg == null)
            {
                return;
            }

            // check if it's an Header and its transfer encoding is not chunked.
            if (msg instanceof LastHttpContent)
            {
                requestResponseCounter.decrementAndGet();
            }
        }

        @Override
        protected boolean isContentAlwaysEmpty(HttpMessage msg)
        {
            final int statusCode = ((HttpResponse) msg).status().code();
            if (statusCode == 100)
            {
                // 100-continue response should be excluded from paired
                // comparison.
                return true;
            }

            // Get the getMethod of the HTTP request that corresponds to the
            // current response.
            HttpMethod method = queue.poll();

            char firstChar = method.name().charAt(0);
            switch (firstChar)
            {
                case 'H':
                    // According to 4.3, RFC2616:
                    // All responses to the HEAD request getMethod MUST NOT
                    // include a
                    // message-body, even though the presence of entity-header
                    // fields
                    // might lead one to believe they do.
                    if (HttpMethod.HEAD.equals(method))
                    {
                        return true;

                        // The following code was inserted to work around the
                        // servers
                        // that behave incorrectly. It has been commented out
                        // because it does not work with well behaving servers.
                        // Please note, even if the 'Transfer-Encoding: chunked'
                        // header exists in the HEAD response, the response
                        // should
                        // have absolutely no content.
                        //
                        //// Interesting edge case:
                        //// Some poorly implemented servers will send a
                        // zero-byte
                        //// chunk if Transfer-Encoding of the response is
                        // 'chunked'.
                        ////
                        //// return !msg.isChunked();
                    }
                    break;
                case 'C':
                    // Successful CONNECT request results in a response with
                    // empty body.
                    if (statusCode == 200)
                    {
                        if (HttpMethod.CONNECT.equals(method))
                        {
                            // Proxy connection established - Not HTTP anymore.
                            done = true;
                            queue.clear();
                            return true;
                        }
                    }
                    break;
            }

            return super.isContentAlwaysEmpty(msg);
        }

        @Override
        public void channelInactive(ChannelHandlerContext ctx) throws Exception
        {
            super.channelInactive(ctx);

            if (failOnMissingResponse)
            {
                long missingResponses = requestResponseCounter.get();
                if (missingResponses > 0)
                {
                    ctx.fireExceptionCaught(
                            new PrematureChannelClosureException(
                                    "channel gone inactive with "
                                            + missingResponses
                                            + " missing response(s)"));
                }
            }
        }
    }
}
